allow reverse proxy auth to provide user full name

[willnorris]

Feature Description

Today, gitea supports external authentication using the reverse proxy auth. It currently supports getting the username and email from the reverse proxy. It would be great if it also supported getting the user's full name from the reverse proxy if it's available.

For example, grafana's external auth supports getting full name (and a handful of other attributes that make sense for them). And similarly, Tailscale's nginx-auth can provide the user's full name. I'm an engineer at Tailscale, and ran into this when setting up gitea on my home network.

I have a working patch and will submit that shortly.

Screenshots

No response